A known palletising device comprises two operating platforms, one of which is superposed over the other, the upper platform being situated along a conveyor line of the products to be palletised, while the lower platform is situated along a line conveying pallets.
The lower platform is associated to an elevator group which vertically moves the platform between a lowered position, in which the platform receives an empty pallet from the conveyor line, and a raised position, in which the platform positions the pallet at a short distance beneath the upper platform.
The upper platform comprises support means having a variable configuration, typically a shutter, which can be shifted by activating means between a closed configuration, in which the support means provide a loading surface which restingly supports the products to be palletised, and an open configuration, in which the support means remove their support, thus allowing the products to fall downwardly under gravity.
When the support means are in a closed configuration, the products to be palletised are loaded on the loading surface horizontally, such as to form a layer of grouped products, after which the support means are brought into an open configuration, so that the layer of products rests directly on the pallet which is borne by the underlying lower platform.
At this point, the lower platform is lowered by an amount which is substantially the same as the height of the products collected together on the pallet, and the support means of the upper platform are brought back to a closed configuration, in order to be able to receive another layer of products.
This cycle is repeated several times, until a complete stack of products is formed on the pallet.
When the operations are terminated, the lower platform is brought back to the initial lowered position, so that the completely loaded pallet can be removed from the conveyor line and sent towards further operating stations, the completely loaded pallet being replaced by an empty pallet.
A drawback of this device arises from the fact that during the removal of the loaded pallet, and its replacement with a fresh empty pallet, the lower platform has to remain constantly in a lowered position, which makes it impossible to commence a new stacking phase.
The document DE 28 08 129 discloses a device in which an intermediate platform is provided between the upper platform and the lower surface, the intermediate platform being associated to activating means which shift it between two fixed positions, namely a raised position under the upper platform and a lowered position over the lower surface on which the pallet is located, and vice versa. The intermediate platform is not suitable for receiving progressively the layers of products resting one on the other.
As a result, these operating phases can only be performed in a strictly sequential way, which means that a somewhat long overall time is necessary in order to terminate the palletising operation.